This invention relates to a control unit for controlling activation of a compressor whose interior is filled with a liquid refrigerant. When a compressor is stopped for a long time, a gaseous refrigerant is liquefied and may enter together with a lubricating oil the compressor and fills its interior, causing the so-called sleeping condition. When the compressor is activated under this condition, the liquid refrigerant and lubricating oil within the compressor are liquid-compressed, possibly breaking the compressor. To prevent this, there have heretofore been provided, measures such as (1) an accumulator is provided to prevent the liquid from entering the compressor, (2) a driven crank is disposed to discharge liquid from the compressor (for example, Japanese Patent Laid-open Print No. 215481/1986 and (3) a relief valve is disposed to release the liquid from the compressor (for example, Japanese Patent Laid-open Print No. 81982/1990, Japanese Laid-open Print No. 193090/1989, and Japanese Patent Laid-open Print No. 23589/1987).
But, the measure above (1) has such drawbacks that the number of parts increases, the of the compressor increases, and that modification the of accumulator the 5 becomes needed with performance increasing. The above measure (2) has such drawbacks that the number of parts increases, the assembling work is difficult, and operation that the lacks reliability. The measure above (3) has such drawbacks that the number of parts increases, the assembling work is troublesome, and that the reliability is low.